1. Field of the Invention
The process and apparatus of this invention relate to the electrolytic recovery of copper or other materials, and more particularly, but not by way of limitation, to electrowinning high purity copper from an aqueous electrolyte.
2. Description of the Prior Art
Electrolysis of copper has been used as a technique for refining copper and for recovering copper from solvents used in copper extraction processes. For example, one process for recovering copper involves subjecting solid materials containing copper to acid or salt leaching followed by extraction purification and electrolytic recovery of the copper from the extraction solvent. Generally, heretofore, impurities such as iron, cobalt, molybdenum, and other compounds contained in the extraction solvent resulted in the recovery of relatively low purity copper in the electrolytic recovery process. The impurities and usual low copper concentration in the solvent have caused the electrolytic recovery process to be of low efficiency and poor recovery.
U.S. Pat. application Ser. No. 332,538 filed Feb. 14, 1973 and assigned to the assignee of this present invention discloses a greatly improved electrolysis process and apparatus for the electrolytic recovery of copper and other metals, which process and apparatus achieve the electrowinning of high purity copper at high efficiency and high current density from liquors or extraction solvents having low copper concentration and containing impurities and gaseous reagents. As described in detail in the application, the process is carried out in apparatus comprising an electrolysis tank containing anode and cathode electrodes immersed in electrolyte contained the electrodes being connected therein, to means for impressing an electric potential between the anode and cathode and through the electrolyte. Means for agitating the electrolyte and controlling the temperature of the electrolyte at a selected level are also provided. A particular novel aspect of the invention of the aforementioned application involves covering the electrolyte in the electrolysis tank with a layer of an immiscible fluid of low conductivity to prohibit gas evolution and misting from the electrolyte and electrolysis tank, as well as preventing oxygen and other impurities from entering the electrolyte from the atmosphere. The process includes circulating the electrolyte through the electrolysis apparatus with the electrolyte continuously being covered by the layer of immiscible non-conductive fluid. In recovering copper from an aqueous acid electrolyte in accordance with the invention, the concentration of sulfur dioxide in the electrolyte is adjusted and controlled by injecting sulfur dioxide thereinto as the electrolyte is circulated. The temperature of the electrolyte is controlled at a selected level and the electric potential impressed between the electrodes brings about the formation of sulfuric acid at the anode and the deposition of high purity copper at the cathode. The cover of low conductivity immiscible fluid on top of the electrolyte prevents sulfur dioxide and other vapors from evolving from the electrolysis tank during the carrying out of the process as well as misting of the electrolyte from the apparatus, etc.
While the above-described process and apparatus have achieved a high degree of success in the recovery of high purity copper and other metals from electrolytes at high efficiency and high current density, problems have been encountered in that the necessary agitation or circulation of the electrolyte causes agitation of the interface between the electrolyte and the covering immiscible liquid resulting in droplets of the immiscible liquid being drawn into the electrolyte. That is, the formation of vortices due to pressure changes and agitation due to fluid movement causes droplets of the immiscible liquid to be drawn into the electrolyte which are emulsified as they are circulated through the system. The build-up of electrolyte-immiscible liquid emulsion in the electrolysis system in turn interferes with the deposition of the metal sought to be recovered and reduces the efficiency of the process.
By the present invention an improved process and apparatus are provided wherein problems relating to the entrainment and emulsification of immiscible covering liquid with the electrolyte are obviated.